Different approach of using IN clause in MySql

Question

Today I have posted an answer with a query like this

SELECT * FROM table_name where column_name IN (val1,val2,...)

Some another user has po

Answer 1

As noted in the question, the MySQL documentation gives the form of the IN clause as:

expr IN (value,...)

expr is an expression that can only have a single value for a given row - this value can be a constant (such as 2), the name of a column (such as column_name from the question) which will have a specific value on a given row, or any expression including functions, operators, constants and column_names that produces a single value for a given row.

The contents of the parentheses - value,... - contains an expression that can be evaluated as supplying a list of values (potentially including an empty list of values, in which case the in condition would be evaluated as false). This list of values could be:

• in the form of an explicit series of one or more constants (such as val1,val2,...) and/or one or more single-valued column names for a given row (such as column_name) and/or a series of expressions that each produce a single value for a given row; or
• in the form of a select clause that returns a set of values (such as select column_name from table where ...) that can then be compared with the value of expr (immediately preceding the IN operator).

To summarise: expr must evaluate to a single value (for a given row), while the parenthesised set of values to be matched can be evaluated to 0, 1 or more values.

In this respect, MySQL operates the same way as any other variant of SQL that I have used.

Where MySQL does vary is that the entire expr IN (value,...) clause itself evaluates to 0 or 1, which MySQL treats as false or true respectively - in most variants of SQL, the entire clause would evaluate to a boolean FALSE or TRUE.

Answer 2

you raised a question that is connected with my answer here.

In a simple explanation using this statements below,

SELECT * FROM TableName WHERE column1 IN (1, 2, 3, 4)
-- versus
SELECT * FROM TableName WHERE 1 IN (column1, column2, column3, column4)

The first statement involves only ONE COLUMN that is being compared to multiple values.

SELECT  *
FROM   TableName
WHERE  column1 = 1 OR
       column1 = 2 OR
       column1 = 3 OR
       column1 = 4

while the second statement is A VALUE that is compared to multiple columns.

SELECT  *
FROM   TableName
WHERE  column1 = 1 OR
       column2 = 1 OR
       column3 = 1 OR
       column4 = 1

which is a bit different from one another.

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UPDATE 1

Here's the third form of IN clause:

• Multi-Column IN clause – Unexpected MySQL Issue